Electrical resistance composition and method of using the same to form a resistor



' A. H. MONES ELECTRICAL RESISTANCE COMPOSITION AND METHOD OF USING THE SAME TO FORM A RESISTOR Filed March 25, 1963 Au 22, 1%? I 3,337,365

15 A Pd ALLOY PARTICLES 14 PdOPARTICLES R x 15 GLASS MATRIX/ 11 CERAMIC BASE/ /HCERAMIcBAsE INVENTOR ARTHUR H. MONES ATTORNEY United States Patent Ofiice 3,337,365 Patented Aug. 22, 1967 3,337,365 ELECTRICAL RESISTANCE COMPOSITION AND METHOD OF USING THE SAME TO FORM A RESISTOR Arthur H. Mones, Poughkeepsie, N.Y., assignor to International Business Machines Corporation, New York, N.Y., a corporation of New York Filed Mar. 25, 1963, Ser. No. 267,643 Claims. (Cl. 117-215) The present invention is directed to electrical resistance compositions, elements, and the method of making them. More particularly, the invention relates to thin film resistance elements, the compositions employed in their fabrication, and the methods of making them.

Electrical resistors have been made by firing a vitreous enamel resistance composition on a ceramic base so as to create a resistive film thereon. In general, such resistors have included a mixture of nonconductive material and conductive metal in a vitreous matrix that is intimately attached to a suitable nonconductive base such as one of ceramic material. The resistance of the resistor is dependent upon the relative proportions of the nonconductive and the conductive materials utilized in the resistive composition. Satisfactory film resistors for many applications have included particles of palladium oxide and a conductive metal such as silver in a glass matrix on a ceramic base. The finely divided silver and palladium oxide, which have been employed as the starting materials for such resistive compositions, have required mechanical mixing that is not as rapid nor as thorough as may be desired. Also, the resistivity and the temperature coefficient of resistance of a resistive film made from such materials are dependent to some extent on the physical parameters of palladium oxide and the silver particles which are employed. For example, the resistivity and the temperature coefiicient of the resistance may undesirably vary by a factor of four or more depending upon the crystallite size and shape of surface area of the palladium oxide and the silver particles. From the fabrication standpoint, it is desirable to reduce this dependence.

High values of resistivity for such films, that is the resistivity in the kilohm region, are obtained by increasing the glass concentration in the mixture of silver and palladium oxide to about 50% While reducing the silver concentration. The reduction of the silver concentration is elfective to increase the load stability but unfortunately reduces thermal stability. Glass in the environment under consideration presents problems. The glass ordinarily has a thermal coefiicient of linear expansion which is quite different from that of the ceramic substrate. Increasing the glass content of the mixture undesirably increases the thermal expansion problem of the resistance film on the substrate so that thermal cycling of the finished resistor may bring about cracking of the film. Such cracking may injure connections to the resistor electrodes and may introduce unwanted discontinuities or interruptions in the resistive film together with insulating barriers of glass that iutroducecapacitance and reduce the capabilities of the resistor at high frequencies. The described increase in the glass content of the composition used in making the film resistor creates a negative temperature coefiicient of resistance which usually requires compensation by a suitable alteration of the silver to palladium oxide ratio. On the other hand, when the concentration of the glass in the resistive composition to be fired on a ceramic base is low, for example, is around 10%, and the silver is omitted as an ingredient of the composition, a resistor having a resistance of the order of 150 ohms per square results which drifts about 10% at 150 C. in one half .hour.

It is an object of the present invention, therefore, to provide a new and improved electrical resistance composition and resistor element which avoid one or more of the above-mentioned shortcomings of prior resistance compositions and elements.

It is a further object of the invention to provide a new and improved electrical resistance film which has good load stability, drift, frequency response, a low temperature coeflicient of resistance, and a good resistor scaling.

It is yet another object of the present invention to provide a new and improved electrical resistance composition for making a film resistor, the resistivity and the temperature coefiicient of resistance of which are less dependent upon the physical parameters of the metallic constituents of the resistance composition than prior such compositions.

It is also an object of the invention to provide a new and improved electrical resistance composition which may include relatively small quantities of glass, such as less than 10% glass.

In accordance with the particular form of the present invention, an electrical resistance composition adapted to be applied to and fired on an electrically nonconductive base comprises a quantity of finely divided material from the group consisting of palladium oxide, palladium chloride and palladium, where the quantity of the palladium oxide is parts, the palladium chloride is 144 parts, and the palladium is 868 parts. The composition further includes a quantity of finely divided material from the group consisting of silver chloride, silver bromide and silver iodide where the quantity of silver chloride is 233-279 parts, the silver bromide is 306-366 parts, and silver iodide is 38-454 parts. The composition also includes 0-400 parts of finely divided glass, and 0-50 parts of finely divided metal oxide from the group consisting of bismuth trioxide and lead oxide.

Also in accordance with the invention, an electrical resistance element comprises an electrically nonconductive base having fired thereon a layer of a resistance composition including finely divided material from the group consisting of palladium oxide, palladium chloride and palladium where the quantity of palladium oxide is 100 parts, the quantity of palladium chloride is 144 parts and the palladium is 86.8 parts. The aforesaid composition further includes a quantity of finely divided material from the group consisting of silver chloride, silver bromide and silver iodide, where the quantity of silver chloride is 233-279 parts, the silver bromide is 30.6-366 parts, and the silver iodide is 38-454 parts. The composition additionally includes 0-400 parts of finely divided glass and 0-50 parts of finely divided metal oxide from the group consisting of bismuth trioxide and lead oxide.

Further in accordance with the present invention, the method of making an electrical resistance element comprises forming a viscous mixture containing a volatile liquid carrier, a quantity of finely divided material from the group consisting of palladium oxide, palladium chloride and palladium, where the quantity of palladium oxide is 100 parts, the palladium chloride is 144 parts and the palladium is 86.8 parts, a quantity of finely divided silver ditionally heating the film to a higher temperature sufficient to decompose thermally the silver halide and release silver, to soften the glass and to form on the aforesaid base an adherent resistive film consisting of palladium oxide and silver-palladium alloy in a glass matrix, and cooling the aforesaid base and the aforesaid adherent resistive film.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawing.

In the drawing:

FIG. 1 is a sectional view to a greatly enlarged scale of a portion of an electrical resistance element in accordance with the present invention; and

FIG. 2 is a similar view of a portion of an electrical resistance element with a protective glass coating thereover.

Electrical resistance element of FIG. 1

Referring now more particularly to FIG. 1, an electrical resistance element in accordance with the invention, includes an electrically nonconductive base 11 of a suitable material such as a ceramic having fired thereon 'a thin layer 12 of a particular resistance composition. The resistance composition comprises a quantity of finely divided material from the group consistingof palladium oxide, palladium chloride and palladium, where the quantity of palladium oxide is 100 parts, the palladium chloride is 144 parts, and the palladium is 86.8 parts. The resistive composition also comprises 38454 parts of a finely divided material from the group consisting of silver chloride, silver bromide and silver iodide, Where the quantity of silver chloride is 235-279 parts, the silver bromide is 30.6-366 parts, and the silver iodide is 38-454 parts. The composition additionally includes 0-400 parts of finely divided glass, and 7.550 parts of a metallic oxide from the group consisting of bismuth trioxide and lead oxide (PbO). Particle sizes such as less than 40-50 microns have proved to be useful.

While palladium chloride and the metal palladium have proved to be useful as ingredients of the resistive composition, palladium oxide has been particularly satisfactory as one of those ingredients. The silver halides, such as silver iodides, silver bromide and silver chloride, which react readily at relatively low temperatures are useful silver compounds, the silver iodide being particularly attractive. While other silver compounds such as silver acetate and silver carbon-ate decompose at around 200 C., they have proved to be unattractive in the formation of resistive compositions, possibly due to the creation of long uninterrupted silver chains which afford too loW a resistance. Lead borosilicate glasses are useful in this en vironment.

The dry resistance composition mentioned above is mechanically mixed in any convenient manner and is then preferably mixed with a suitable inert liquid vehicle so as to form a viscous mixture or paste. The liquid vehicle may be glycerin or an organic solvent such as methyl, ethyl, butyl, or propyl alcohol. It has been found that a relatively low concentration of finely divided or colloidal silicon dioxide promotes a mixing of the several ingredients of the composition or viscous mixture. It is also quite beneficial to employ a somewhat larger quantity of bismuth trioxide or lead oxide than the silicon dioxide to promote cohesion of the various materials constituting the viscous mixture, and to further the adhesion of the mixture to the ceramic base 11 in a filming operation presently to be described. The viscous mixture is formed into a film on the ceramic base by a suitable technique such as by silk screening. The structure thus formed is mildly heated to an intermediate temperature such as about 110 C. to drive off or volatilize the vehicle and any contaminants which might be in the paste, thus leaving a dry film on the ceramic base 10. Next the structure is fired in an oven at a higher temperature such as one in the range of 600-850 C. for a period of about 10' minutes, and is then removed from the oven and preferably slowly cooled over a period such as about 30 minutes. Alternatively, the cooling may be accomplished quickly in about 2 minutes. The selected high temperature is determined in part by the softening temperature of the finely divided glass which is employed in the viscous mixture.

The described operation of heating the dried film at a temperature such as 750 C. thermally decomposes the silver halide and also the palladium chloride, when the latter is an ingredient of the mixture. The silver halide that is employed serves a dual purpose. First it fluxes a reaction, that is, it facilitates the silver and palladium which are released from the compound or compounds in the formation of particles that consist of a silver-palladium alloy 13. Secondly, the silver halide provides by its decomposition the silver required for forming that alloy. The decomposition of the silver compound to release silver may also be looked upon as a sort of a chemical mixing operation which makes the silver available in a form wherein it will alloy more readily with the available palladium to form the silver-palladium alloy particles 13. In addition to forming the alloy particles just mentioned, palladium oxide particles 14 are also formed. These two types of particles are contained in a glass matrix 15.

It is believed that the film 12 which is established on the ceramic base has a structure similar to that represented diagrammatically in FIG. 1. The palladium oxide particles are semiconductive in character and individual ones are believed to be encompassed by individual ones of the silver-palladium alloy particles. Their distribution in the glass matrix is deemed to be such that the film 13 has a resistivity which is dependent upon the relative proportions of the starting materials that are employed to form the silver-palladium alloy particles 13, the palladium oxide particles 14, and the glass matrix 15. The resistivity of film 12 is conveniently altered by changing the silver-palladium ratio. For example, a low resistivity may be achieved by increasing the number of parts of the silver halide employed to supply the silver for the silverpalladium alloy. Conversely, increasing the quantity of palladium compound such as palladium oxide or increasing the quantity of glass will provide a higher resistivity film.

The following chart is helpful in showing a range of suitable ingredients which have proved to be useful in the formation of several resistive compositions for application and firing on a ceramic base.

Preierred Good Suitable Resistance films having resistivities from S0 to 30 kilohms per square have been produced from various proportions of the materials identified above. The load stability of such films has range from good to excellent. By load stability, one means that the translation of power through the resistiive film does not cause the latter to deteriorate. When resistors which are made from films of the type under consideration were held at a temperature of C. for short periods, such as about 50 hours, the drift in resistance was quite low and in the range of 0.1 to 0.2%. Such resistors have exhibited less than a 10% variation in resistance at frequencies up to 100 megacycles. Resistors using resistance films of the invention are characterized by a low temperature coefiicient of resistance designated TCR. A few examples of the results which have been obtained are as follows:

Resistivity in ohms/ square: TCR, ppm. 100 100 20,000 -40 500,000 -300 Electrical resistance element of FIG. 2

Because the resistive film 12 that is produced on the ceramic base 11 of FIG. 1 is not a tough hard film, it is sometimes desirable to provide it with abrasion protection by covering it With a protective coating 16 of vitreous bonding material such as a borosilicate or other high melting point glass. Finely divided glass in a suitable vehicle to provide a viscous mixture may be applied to the film 12 by a well-known silk-screening operation. The coating 16 is then heated to a temperature slightly above the softening temperature of the glass particles so as to form a continuous jacket which is bonded to the film 12. In addition to providing abrasive protection and a seal for the glass film 12, the vitreous coating 16 afi'ords an additional benefit, the reasons for which are not presently understood. It has been found that the coating 16 serves to improve the temperature coefficient of resistance of the electrical resistance element. Ideally, such a device would have a zero temperature coefficient of resistance in parts per million per degree centigrade. The glass coating 16 is eifective in providing a significantly better temperature coeflicient of resistance for the resistance element covered thereby.

Although terminals have not been shown in FIGS. 1 and 2 for the electrical resistance elements thereof, it will be manifest to one skilled in the art that such a device would be provided with suitable terminals as by the application of a colloidal metal paste and conductors to the ends of the resistive film.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. An electrical resistance composition adapted to be applied to and fired on an electrically nonconductive base comprising:

a quantity of finely divided material from the group consisting of palladium oxide, palladium chloride, and palladium, Where the quantity of palladium oxide is 100 parts, the palladium chloride is 144 parts, and the palladium is 86.8 parts;

a quantity of finely divided material from the group consisting of silver chloride, silver bromide and silver iodide, where the quantity of silver chloride is 23.3- 279 parts, the silver bromide is 306-366 parts, and the silver iodide is 38-454 parts;

0-400 parts of finely divided glass; and

0-50 parts of finely divided metal oxide from the group consisting of bismuth trioxide and lead oxide.

2. An electrical resistance composition adapted to be applied to [and fired on an electrically nonconductive base comprising:

a quantity of finely divided material from the group consisting of palladium oxide, palladium chloride, and palladium, where the quantity of palladium oxide is 100 parts, and the quantities of palladium chloride and palladium are the chemical equivalent of 100 parts of said oxide;

a quantity of finely divided material from the group consisting of silver chloride, silver bromide and silver iodide, where the quantity of silver chloride is 233-279 parts and the quantities of silver bromide and silver iodide are the chemical equivalents of 23.3-279 parts of silver chloride;

0-400 parts of finely divided glass; and

0-50 parts of finely divided metal oxide from the group consisting of bismuth trioxide and lead oxide.

3. An electrical resistance composition in accordance with claim 2 in combination with sufficient inert liquid vehicle to form a paste.

4. An electrical resistance composition adapted to be applied to and fired on an electrically nonconductive base comprising:

a quantity of finely divided material from the group consisting of palladium oxide, palladium chloride, and palladium, Where the quantity of palladium oxide is parts, the palladium chloride is 144 parts, and the palladium is 86.8 parts;

a quantity of finely divided material from the group consisting of silver chloride, silver bromide and silver iodide, where the quantity of silver chloride is 233-279 parts, the silver bromide is 306-366 parts, and the silver iodide is 38-454 parts;

0-400 parts of finely divided glass;

0-50 parts of finely divided metal oxide from the group consisting of bismuth trioxide and lead oxide; and

0-25 parts of finely divided silicon dioxide.

5. An electrical resistance composition adapted to be applied to and fired on an electrically nonconductive base comprising:

a quantity of finely divided material from the group consisting of palladium oxide, palladium chloride, and palladium, where the quantity of palladium oxide is 100 parts, the palladium chloride is 144 parts, and the palladium is 86.8 parts;

38-454 parts of finely divided silver iodide;

0-400 parts of finely divided glass; and

0-50 parts of finely divided metal oxide from the group consisting of bismuth trioxide and lead oxide.

6. An electrical resistance composition adapted to be applied to and fired on an electrically nonconductive base comprising:

.a quantity of finely divided material from the group consisting of palladium oxide, palladium chloride, and palladium, where the quantity of palladium oxide is 100 parts, the palladium chloride is 144 parts, and the palladium is 86.8 parts;

-a quantity of finely divided material from the group consisting of silver chloride, silver bromide and silver iodide, where the quantity of silver chloride is 233-279 parts, the silver bromide is 30.6-366 parts, and the silver iodide is 38-454 parts;

0-400 parts of finely divided glass; and

7.5-25 parts of finely divided bismuth trioxide.

7. An electrical resistance composition adapted to be applied to and fired on an electrically nonconductive base comprising:

100 parts of finely divided palladium oxide;

38-454 parts of silver iodide;

0-400 parts of finely divided glass; and

7.5-25 parts of finely divided bismuth trioxide.

8. An electrical resistance composition in accordance with claim 7 in combination with sufiicient inert liquid vehicle to form a paste.

9. An electrical resistance composition adapted to be applied to and fired on an electrically nonconductive base comprising:

100 parts of finely divided palladium oxide;

38-454 parts of silver iodide;

25 parts of finely divided glass; and

25 parts of finely divided bismuth trioxide.

10. An electrical resistance composition adapted to be applied to and fired on an electrically nonconductive base comprising:

100 parts of finely divided palladium oxide;

177 parts of silver iodide;

25 parts of finely divided glass; and

25 parts of finely divided bismuth trioxide.

11. An electrical resistance composition adapted to be applied to and fired on an electrically nonconductive base comprising:

100 parts of finely divided palladium oxide;

454 parts of silver iodide;

25 parts of finely divided glass;

25 parts of finely divided bismuth trioxide; and

13 parts of finely divided silicon dioxide.

12. The method of making an electrical resistance element comprising:

forming a viscous mixture containing a volatile liquid carrier, a quantity of finely divided material from the group consisting of palladium oxide, palladium chloride, and palladium, Where the quantity of palladium oxide is 100 parts, the palladium chloride is 144 parts and the palladium is 86.6 parts, a quantity of finely divided halide from the group consisting of silver chloride, silver bromide and silver iodide, where the quantity of silver chloride is 23.3279 parts, the silver bromide is 30.6366 parts, and the silver iodide is 38-454 parts, -400 parts of finely dividedglass, and 050 parts of finely divided metal oxide from the group consisting of bismuth trioxide and lead oxide;

forming said mixture into a film on an electrically nonconductive base;

heating said film to an intermediate temperature to remove said liquid carrier;

additionally heating said film to a higher temperature sufiicient to decompose thermally said silver halide and release silver, to soften said glass and said metal oxide and to form on said base an adherent resistive film consisting of palladium oxide and silver-palladium alloy in a glass matrix; and cooling said base and said adherent resistive film.

13. The method of making an electrical resistance element comprising:

forming a viscous mixture containing a volatile liquid carrier, a quantity of finely divided material from the group consisting of palladium oxide, palladium chloride and palladium, where the quantity of palladium oxide is 100 parts, the palladium chloride is 144 parts and the palladium is 86.8 parts, a quantity of finely divided halide from the group consisting of silver chloride, silver bromide and silver iodide, where the quantity of silver chloride is 233-279 parts, the silver bromide is 30.6366 parts, and the silver iodide is 38454 parts, 0-400 parts of finely divided glass and 050 parts of finely divided metal oxide from the group consisting of bismuth trioxide and lead oxide;

forming said mixture into a film on an electrically nonconductive base;

heating saidfilm to an intermediate temperature to remove said liquid carrier;

additionally heating said film to a higher temperature sufficient to decompose thermally said silver halide and release silver, to soften said glass and said metal oxide and to form on said base an adherent resistive film consisting of palladium oxide and silver-palladium alloy in a glass matrix;

cooling said base and said adherent resistive film;

forming a viscous mixture containing a volatile liquid carrier and finely divided glass;

forming said last-mentioned viscous mixture into a film on said resistive film;

heating said last-formed film to an intermediate tem perature to remove said last-mentioned liquid carrrer;

heating the modified last-formed film above the temperature of the finely divided glass therein to form a continuous glass film over said resistive film; and

cooling the resultant structure to produce said resistance element.

14. The method of making an electrical resistance element comprising:

forming a viscous mixture containing a volatile liquid carrier, parts of finely divided palladium oxide, 38-454 parts of finely divided silver iodide, 0-400 parts of finely divided glass, and 025 parts of finely divided bismuth trioxide;

forming said mixture into a film on an electrically nonconductive base;

heating said film to a temperature of about C. to

remove said liquid carrier;

additionally heating said film to a temperature of about 750 C. to decompose thermally said silver iodide and release silver, to soften said glass and said hismuth trioxide, and to form on said base an adherent resistive film consisting of palladium oxide and silver-palladium alloy in a glass matrix; and

cooling said base and said adherent resistive film.

15. The method of making an electrical resistance element comprising:

forming a viscous mixture containing a volatile liquid carrier, 100 parts of finely divided palladium oxide, 38454 parts of finely divided silver iodide, 0-25 parts of finely divided glass, and 7.5-400 parts of finely divided bismuth trioxide;

forming said mixture into a film on an electric-ally nonconductive base;

heating said film to a temperature of about 110 C.

to remove said liquid carrier;

additionally heating said film to a temperature of about 750 C. to decompose thermally said silver iodide and release sliver, to soften said glass and said bismuth trioxide, and to form on said base an adherent resistive film consisting of palladium oxide and silver-palladium alloy in a glass mixture;

cooling said base and said adherent resistive film;

forming a viscous mixture containing a volatile liquid carrier and finely divided glass;

forming said last-mentioned viscous mixture into a film on said resistive film;

heating said last-formed film to a temperature of about 110 C. to remove said last-mentioned liquid carrier;

heating the modified last-formed film above the softening temperature of the finely divided glass therein to form a continuous glass film over said resistive film; and cooling the resultant structure to produce said resistance element.

References Cited UNITED STATES PATENTS 2,328,101 8/1943 Rosenblatt 117-123 2,924,540 2/1960 DAndrea 252-514 3,052,573 9/1962 Durnesnil 117227 3,149,002 9/1964 Place et a1. 117123 FOREIGN PATENTS 1,132,220 6/1962 Germany.

ALFRED L. LEAVITT, Primary Examiner.

WILLIAM L, JARVIS, Examiner. 

12. THE METHOD OF MAKING AN ELECTRICAL RESISTANCE ELEMENT COMPRISING: FORMING A VISCOUS MIXTURE CONTAINING A VOLATILE LIQUID CARRIER, A QUNTITY OF FINELY DIVIDED MATERIAL FROM THE GROUP CONSISTING OF PALLADIUM OXIDE, PALLADIUM CHLORIDE, AND PALLADIUM, WHERE THE QUANTITY OF PALLADIUM OXIDE IS 100 PARTS, THE PALLADIUM CHLORIDE IS 144 PARTSS AND THE APLLADIUM IS 86.6 PARTS, A QUANTITY OF FINELY DIVIDED HALIDE FROM THE GROUP CONSISTING OF SILVER CHLORIDE, SILVER BROMIDE AND SILVER IODIDE, WHERE THE QUANTITY OF SIVER CHLORIDE IS 23.3-279 PARTS, THE SILVER BROMIDE IS 30.6-366 PARTS, AND THE SILVER IODIDE IS 38-454 PARTS, 0-400 PARTS OF FINELY DIVIDED GLASS, AND 0-50 PARTS OF FINELY DIVIDED METAL OXIDE FROM THE GROUP CONSISTING OF BISMUTH TRIOXIDE AND LEAD OXIDE; FORMING SAID MIXTURE INTO A FILM ON AN ELECTRICALLY NONCONDUCTIVE BASE; HEATING SAID FILM TO AN INTERMEDIATE TEMPERATURE TO REMOVE SAID LIQUID CARRIER; ADDITIONALLY HEATING SAID FILM TO A HIGHER TEMPERATURE SUFFICIENT TO DECOMPOSE THERMALLY SAID SILVER HALIDE AND RELEASE SILVER, TO SOFTEN SAID GLASS AND SAID METAL OXIDE AND TO FORM ON SAID BASE AN ADHERENT RESISTIVE FILM CONSISTING OF PALLADIUM OXIDE AND SILVER-PALLADIUM ALLOY IN A GLASS MATRIX; AND COOLING SAID BASE AND SAID ADHERENT RESISTIVE FILM. 